1. Field of the Invention
The present invention relates to a two screw double-stroke and screw differential-motion mechanism applied in a standard mechanical interface and, in particular, to one that utilizes the correlation of transmission between screws and nuts and the screw differential-motion so as to achieve double-stroke and differential-motion effects.
2. Description of the Prior Art
Due to spatial limits, expensive maintenance fees for clean rooms, and stringent requirements on cleanness in a semiconductor fab, the concept of a standard mechanical interface (SMIF) and machine design has been established and developed to classify clean rooms of different levels that machines or operators can access so as to decrease the chance of particle pollution, to increase the cleanness of clean rooms, to lower maintenance fees, and to increase IC wafer yield. In particular, the design of an SMIF arm appears more important. When the SMIF arm is combined with process equipment, the transmission arm has to move forward to the process equipment and grasp a cassette with a clamp. When the arm returns, it should go back to the center of the process equipment. Therefore, the clamp has to travel about twice the distance that the screw can proceed. Furthermore, there is a higher demand for cleanness in current IC wafer process environments.
With clamps, the heavier the clamp is, the more vibration there is in mechanical motions. Furthermore, the more motion links there are, the more likely there will be particle production and machine wiggles. Some conventional SMIF arm designs make use of an elbow-arm mechanism and complete the retrieval and placement of a cassette using clamp motion along the z-axis (e.g. the ASIST""s design). Some have a linkless air pressurized cylinder mechanism installed on the inner side of the machine to drive the clamp back and forth for retrieving and placing the cassette (e.g. the INFAB""s design). Or a set of mechanical arms may be mounted above the machine with extension and flexion mechanisms to achieve the retrieval and placement of a cassette (e.g. the FORTREND""s design). Alternatively, a single screw may be installed on the inner side of the machine to obtain, in conjunction with a timing belt pulley, a double-stroke clamp for the retrieval and placement of a cassette (e.g. the one by Industrial Technology Research Institute, Mechanical Industry Research Laboratories). However, the above-mentioned mechanisms are either so complicated that more friction exists in machine operations and more waste particles are produced, or too expensive in production and maintenance costs.
In view of the foregoing, it is highly desirable to have a mechanism that can prevent waste particle production, effectively isolate the particles, and simplify the design of the machine.
It is an object of the present invention to provide a two screw double-stroke and screw differential-motion mechanism applied in a standard mechanical interface. The two screw double-stroke mechanism adopts a two screw connection mechanism to achieve the goal of double strokes; therefore the longitudinal depth of the machine can be decreased by about xc2xd. Thus, the space require by the machine is greatly reduced. Compared with current products on the market, the present invention has a smaller size, stronger mechanism rigidity, longer stroke, and smaller space occupied by the arm.
It is another object of the present invention to provide a two screw double-stroke and screw differential-motion mechanism applied in a standard mechanical interface, whose two screws double-stroke mechanism uses an outer cover to enclose the transmission mechanism of the SMIF arm so as to greatly reduce particle production and diffusion.
It is yet another object of the present invention to provide a two screw double-stroke and screw differential-motion mechanism applied in a standard mechanical interface, whose two screw double-stroke mechanism has an optimized design between the linear tracks and screws so that by mutual support, fixture, and sliding the rigidity of the motional elements can be greatly increased and fewer vibrations would happen to the end of the retrieval mechanism.
It is a fourth object of the present invention to provide a two screw double-stroke and screw differential-motion mechanism applied in a standard mechanical interface, wherein due to the transmission consistency of the transmission axle the screw differential-motion mechanism can diminish the probability of clamp retrieval errors.
It is a fifth object of the present invention to provide a two screw double-stroke and screw differential-motion mechanism applied in a standard mechanical interface, wherein the screw differential-motion mechanism has such a simple structure that the weight of the end-point clamp and the complexity of the mechanism can be greatly decreased and thus the invention can reduce the vibrations and inertia of the mechanism.
It is a further object of the present invention to provide a two screw double-stroke and screw differential-motion mechanism applied in a standard mechanical interface, wherein components of the screw differential-motion mechanism have less contact that there is less production of waste particles due to friction.
The two screw double-stroke and screw differential-motion mechanism applied in a standard mechanical interface with the above features comprises:
a two screw double-stroke mechanism, whose inside is a fixed substrate mounted with a guide rack, the contact surface of said guide rack and said fixed substrate being provided with a set of linear track; a driving motor, which is mounted inside said guide rack and drives through a timing belt a power transmission timing belt pulley fixed within said guide rack, said power transmission timing belt being installed on a ball screw nut and combined with said guide rack using angular contact ball bearings; an end-point timing belt pulley, which is mounted on the side of a screw opposite to a screw nut and drives said screw into rotation with the power transmitted from said power transmission timing belt pulley, said screw nut performing horizontal sliding at the same time; and
a screw differential-motion mechanism, which is provided above said screw nut and comprises a driving motor for driving a differential screw with a left thread and a right thread on both ends, each end of said differential screw having therein a clamp means containing a female thread fitting with both ends of said differential screw, two sets of linear tracks at the bottom of said clamp means, and a hook on each side of said screw differential-motion mechanism for horizontal motion in conjunction with said clamp means.